Rains causing more malaria despite use of nets, Kemri says

The changing climate has a stronger effect on the spread of malaria than the use of bed nets, which is currently the main way to control the disease in Kenya.

Researchers from the Kenya Medical Research Institute, who analysed the monthly incidence of malaria from 2008-2019, found that heavy rains always lead to more malaria cases in Western Kenya, regardless of the high usage of bed nets.

Insecticide-treated bed nets are the primary preventive tool in high-burden areas such as the Lake Victoria region, where the study was done.

“Variability in climatic factors showed a stronger effect on malaria incidence than bed net use,” they said in their final results, which will be published in the Parasite Epidemiology and Control journal next month.

The results are important because they mean Kenya must go beyond bed nets and incorporate climate-based warning systems to prevent malaria.

Still, the authors, who include Kemri’s Bryan Nyawanda, said bed nets are extremely useful in reducing the spread of malaria.

“To sustain the downward trend in malaria incidence, this study recommends continued distribution and use of bed nets and consideration of climate-based malaria early warning systems when planning for future control interventions,” Nyawanda and his colleagues said.

They analysed data from the Lwak Mission Hospital between 2008 and 2019.

The analysis showed that malaria incidence decreased by 73 per cent from 2010 until 2015, largely due to the increased use of bed nets.

“There was a resurgence of cases after 2016, despite high bed net use,” they said.

The region received heavy rains in 2016 due to the El Nino climate phenomenon.

The researchers also noted an increase in daytime land surface temperature was associated with a decline in malaria incidence.

Malaria incidence in Kenya has a bimodal seasonality, with the first and more pronounced peak during May–July, and the second peak during November-January.

“An increase in rainfall by 10mm was associated with a four per cent increase in malaria incidence,” the researchers said.

The rest are Kemri’s Sammy Khagayi, Godfrey Bigogo, David Obor, Nancy Otieno,  Simon Kariuki and Stephen Munga.

Others are Anton Beloconi, Jürg Utzinger and Penelope Vounatsou from the Swiss Tropical and Public Health Institute;  Stefan Lange from Potsdam Institute for Climate Impact Research; Jonas Franke of Germany’s Remote Sensing Solutions, and Rainer Sauerborn from Heidelberg Institute of Global Health of Germany.

Their study is titled, “The relative effect of climate variability on malaria incidence after scale-up of interventions in western Kenya: A time-series analysis of monthly incidence data from 2008 to 2019.”

Most global climate models show temperatures and rainfall will increase with time.

While high temperatures may reduce malaria prevalence in Western Kenya, where mosquitoes will struggle to survive, it will make currently cooler places such as Mt Kenya areas conducive for mosquito breeding.

Malaria prevalence countrywide is six per cent, according to the 2020 Kenya Malaria Indicator Survey.

But the prevalence is high at 19 per cent in the lake region, which includes Siaya, Kisumu, Migori, Homa Bay, Kakamega, Vihiga, Bungoma and Busia counties.

The coastal region is at five per cent and the low risk areas like Nairobi, Nakuru, Naivasha, Nyeri, Muranga and Machakos have only less than one per cent.

The number of malaria cases seen in hospitals in Kenya every year is 4.6 million.

However, Kenya faces the threat of malaria from new vectors.

Last year, experts from the the Ministry of Health and Kemri also confirmed the presence of a new malaria-causing mosquito known as anopheles stephensi.

The species, the experts said, has been spotted in Marsabit's Saku and Laisamis constituencies, allaying fears it is drug-resistant and not easy to kill.

-Edited by SKanyara